Teach your grandmother to suck eggs, Attempt to teach your elders.
-Brewer's Dictionary of Phrase and Fable, 1963, p. 322.
I'm sure my grandmother, possibly both grandmothers, knew how to suck an egg out. I have a vague recollection of my father telling me about this, possibly even demonstrating, although I can't be sure. But when I saw it done by my favorite Sicilian detective, I knew exactly what it was.
I've been searching for the expression, and coming up against wrong information. Sucking an egg is not separating out the yolk or blowing out an egg. It may well not have been commonly written down, which keeps it out of dictionaries.
I grew up with the expression, and it's been running through my mind a lot lately. As young scrubs try to tell me how to circulate, and not in a "you may have missed this thing I can see" way, but in a "you idiot, I know better, do this" way. I try to take the information and ignore the attitude, but it gets exhausting. I don't want to stifle their observations, often the scrub standing aside as we position can see details easily missed by those of us standing too close. Their interpretations and solutions are almost always wrong, because they don't have the training or experience. Ignorance just don't know what it don't know, ya know?
There does need to be a corollary, of course. Say, The young have sharper eyes, let them find the eggs.

